Emergency evacuation systems in accordance with class A comprise signalling devices wired in a loop comprising a signalling line. In case of evacuation, the loop is provided with an evacuation signal from a base station. The loop comprises isolator devices like the Astrea isolator type ASB-11 till 22. The isolator devices are connected by the signalling line. The loop wiring comprises two conductors like a pair of wires or a coax cable. The loop wiring is interrupted by the isolator. The isolator receives a signal on a receiving module via the signalling line.
Upon reception of the signal, the signal is retransmitted via a sending unit. The quality of the signal sent out is tested. In case the quality of the signal does not meet certain quality standards with respect to for example voltage and/or current, the sending of the signal is interrupted as an out of spec voltage and/or current may indicate a short or open in a signalling line that is part of the loop. Subsequently, the loop is fed from the other side via signalling lines in the loop that are still in good state. The loop is set up as a single loop, over which one analogue audio signal is provided